Ultrasound catheter having protective feature against breakage

ABSTRACT

An ultrasound catheter has an elongate flexible catheter body having a lumen extending longitudinally therethrough, and an ultrasound transmission member extending longitudinally through the lumen of the catheter body. The ultrasound transmission member has a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, with at least a portion of the distal end of the ultrasound transmission member extending outside the lumen of the catheter body and beyond the distal end of the catheter body, and with the ultrasound transmission member directly attached to the catheter body via an attachment device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to medical equipment, and more particularly, to a therapeutic ultrasound system for ablating obstructions within tubular anatomical structures such as blood vessels. The ultrasound system includes a protective feature that minimizes the introduction of debris into the patient's vasculature if the ultrasound transmission member were to break, fracture or become dislodged during a medical procedure.

2. Description of the Prior Art

A number of ultrasound systems and devices have heretofore been proposed for use in ablating or removing obstructive material from blood vessels. Ultrasound catheters have been utilized to ablate various types of obstructions from blood vessels of humans and animals. Successful applications of ultrasound energy to smaller blood vessels, such as the coronary arteries, requires the use of relatively small diameter ultrasound catheters which are sufficiently small and flexible to undergo transluminal advancement through the tortuous vasculature of the aortic arch and coronary tree. However, because of its small diameter, the ultrasound transmission member which extends through such catheters is particularly susceptible to losses in the transmitted ultrasound energy, and breakage.

Breakage of ultrasound transmission members often occurs near the proximal end thereof, generally at the coupling between the ultrasound catheter coupling and the ultrasound transducer. This is believed to be because energy concentrations and stresses are highest at these points. Thus, any external forces applied to the ultrasound transmission member in this region may result in stresses exceeding the elastic limit of the ultrasound transmission member.

External forces may be inadvertently and undesirably applied to the ultrasound transmission member by pressing upon, pushing, pulling, torquing, bending or bumping the ultrasound transmission member coupling during use of the ultrasound catheter. Such forces when applied to the ultrasound catheter coupling area further result in limited ultrasound energy transmission through the ultrasound transmission member. If ultrasound energy is being transmitted by the ultrasound transmission member at the instant such forces are applied thereto, additional stresses occur which may result in breakage of the ultrasound transmission member.

Breakage of ultrasound transmission members can also occur near the distal end thereof, generally at the area of the smallest cross-section. Therefore, it is important that any debris resulting from the breakage of the ultrasound transmission member not be allowed to be introduced into a patient's vasculature during a medical procedure.

Thus, there still exists a need to protect against breakage of the ultrasound transmission member during a medical procedure.

SUMMARY OF THE DISCLOSURE

It is an object of the present invention to provide an ultrasound catheter system with a protective feature that prevents or minimizes the introduction of debris into the patient's vasculature if the ultrasound transmission member were to break or fracture during a medical procedure.

In order to accomplish the objects of the present invention, there is provided an ultrasound catheter having an elongate flexible catheter body having a lumen extending longitudinally therethrough, and an ultrasound transmission member extending longitudinally through the lumen of the catheter body. The ultrasound transmission member has a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, with at least a portion of the distal end of the ultrasound transmission member extending outside the lumen of the catheter body and beyond the distal end of the catheter body, and with the ultrasound transmission member directly attached to the catheter body via an attachment device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an ultrasound system according to the present invention.

FIG. 2 is a cross-sectional view of the distal end of an ultrasound catheter that can be used with the system of FIG. 1 according to one embodiment thereof.

FIG. 3 is a side sectional view of an ultrasound transmission member that can be used with the system of FIG. 1.

FIGS. 4-9 are cross-sectional views of the distal end of various ultrasound catheters that can be used with the system of FIG. 1 according to different embodiments thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims. In certain instances, detailed descriptions of well-known devices, compositions, components, mechanisms and methods are omitted so as to not obscure the description of the present invention with unnecessary detail.

FIG. 1 illustrates an ultrasound system according to the present invention for use in ablating and removing occlusive material inside the vessel of an animal or human. Referring to FIGS. 1 and 2, the ultrasound system includes an ultrasound catheter device 10 which has an elongate catheter body 11 having a proximal end 12, a distal end 14, and defining at least one lumen 15 extending longitudinally therethrough. The ultrasound catheter device 10 is operatively coupled at its proximal end 12, by way of a Y-connector 18, a catheter knob 20, and a slide collar 22, to an ultrasound transducer 24. The ultrasound transducer 24 is connected to a signal generator 26, which can be provided with a foot actuated on-off switch 28. The signal generator 26 can be supported by an IV pole 27. When the on-off switch 28 is depressed, the signal generator 26 sends an electrical signal to the ultrasound transducer 24, which converts the electrical signal to ultrasound energy. Such ultrasound energy subsequently passes through the catheter device 10 and is delivered to the distal end 14. A guidewire 25 may be utilized in conjunction with the catheter device 10, as will be more fully described below.

The catheter body 11 is formed of a flexible polymeric material such as nylon (Pebax™) manufactured by Atochimie, Cour be Voie, Hauts Ve-Sine, France. The flexible catheter body 11 is preferably in the form of an elongate tube having one or more lumens extending longitudinally therethrough. The catheter body 11 defines a main lumen 15. Extending longitudinally through the main lumen 15 is an elongate ultrasound transmission member 16 having a proximal end which is removably connectable to the ultrasound transducer 24 via a sonic connector (not shown) such that ultrasound energy will pass through the ultrasound transmission member 16. As such, when the foot actuated on-off switch 28 operatively connected to the ultrasound transducer 24 is depressed, ultrasound energy will pass through the ultrasound transmission member 16 to the distal end 14 of the catheter body 11.

A guidewire port 58 is provided in the catheter body 11 at any location along the catheter body 11. A guidewire lumen 60 extends from the guidewire port 58 through the main lumen 15 of the catheter body 11 in a manner that is concomitant to the length of the ultrasound transmission member 16. In one embodiment, the guidewire port 58 can be provided at a location that is closer to the proximal end 12 than to the distal end 14 of the catheter.

In one embodiment, the ultrasound transmission member 16 may be formed of any material capable of effectively transmitting the ultrasonic energy from the ultrasound transducer 24 to the distal end 14 of the ultrasound transmission member 16, and is preferably made from metal or metal alloys. It is possible to form all or a portion of the ultrasound transmission member 16 with one or more materials which exhibit super-elasticity. Such materials should preferably exhibit super-elasticity consistently within the range of temperatures normally encountered by the ultrasound transmission member 16 during operation of the catheter device 10. Specifically, all or part of the ultrasound transmission member 16 may be formed of one or more metal alloys known as “shape memory alloys”.

Examples of super-elastic metal alloys which are usable to form the ultrasound transmission member 16 of the present invention are described in detail in U.S. Pat. No. 4,665,906 (Jervis); U.S. Pat. No. 4,565,589 (Harrison); U.S. Pat. No. 4,505,767 (Quin); and U.S. Pat. No. 4,337,090 (Harrison). The disclosures of U.S. Pat. Nos. 4,665,906; 4,565,589; 4,505,767; and 4,337,090 are expressly incorporated herein by reference insofar as they describe the compositions, properties, chemistries, and behavior of specific metal alloys which are super-elastic within the temperature range at which the ultrasound transmission member 16 of the present invention operates, any and all of which super-elastic metal alloys may be usable to form the super-elastic ultrasound transmission member 16.

The frontal portion of the Y-connector 18 is connected to the proximal end 12 of the catheter 10 using techniques that are well-known in the catheter art. An injection pump 54 or IV bag (not shown) or syringe (not shown) can be connected, by way of an infusion tube 55, to an infusion port or sidearm 72 of the Y-connector 18 (see FIG. 1). The injection pump can be used to infuse coolant fluid into and/or through the main lumen 15 of the catheter 10, with the coolant fluid exiting via irrigation outlets 32 (see FIG. 2) provided adjacent the distal end 14 of the catheter 10. Such flow of coolant fluid may be utilized to prevent overheating of the ultrasound transmission member 16 extending longitudinally through the main lumen 15. Such flow of the coolant fluid through the main lumen 15 of the catheter 10 also serves to bathe the outer surface of the ultrasound transmission member 16, thereby providing for an equilibration of temperature between the coolant fluid and the ultrasound transmission member 16. Thus, the temperature and/or flow rate of coolant fluid may be adjusted to provide adequate cooling and/or other temperature control of the ultrasound transmission member 16. The irrigation fluid can include a pharmacological agent and/or microbubbles.

In addition to the foregoing, the injection pump 54 or syringe may be utilized to infuse a radiographic contrast medium into the catheter 10 for purposes of imaging. Examples of iodinated radiographic contrast media which may be selectively infused into the catheter 10 via the injection pump 54 are commercially available as Angiovist 370 from Berlex Labs, Wayne, N.J. and Hexabrix from Malinkrodt, St. Louis, Mo.

The proximal end of the Y-connector 18 is attached to the distal end of the catheter knob 20 by threadably engaging the proximal end of the Y-connector 18 inside a threaded distal bore (not shown) at the distal end of the catheter knob 20.

The proximal end of the ultrasound transmission member 16 is attached to a sonic connector (not shown) which is configured to effect operative and removable attachment of the proximal end of the ultrasound transmission member 16 to the horn of the ultrasound transducer 24. The sonic connector is preferably configured and constructed to permit passage of ultrasound energy through the ultrasound transmission member 16 with minimal lateral side-to-side movement of the ultrasound transmission member 16 while, at the same time, permitting unrestricted longitudinal forward/backward vibration or movement of the ultrasound transmission member 16. Examples of ultrasound transducers, sonic connectors and their connections are illustrated in U.S. Pat. Nos. 6,702,748, 6,855,123, 6,942,620 and 6,942,677, whose disclosures are incorporated by this reference as though set forth fully herein.

Referring to FIGS. 2 and 3, the ultrasound transmission member 16 can have progressively tapered regions extending from the proximal end 34 thereof to the distal tip 36 thereof. For example, the proximal-most region 38 can have a constant diameter which is the greatest diameter along the length of the ultrasound transmission member 16. The region 38 transitions at its distal end to a first tapered region 40 which gradually decreases in diameter to its distal end to a second tapered region 42, which gradually decreases in diameter to its distal end to a third tapered region 44, which gradually decreases in diameter to its distal end to the distal tip 36. Each tapered region 40, 42, 44 can have a continuous taper, and be tapered to different degrees, such that the region 40 has a greater taper than the region 42, which in turn has a greater taper than the region 44. The distal-most part of the region 44 can have the smallest diameter along the entire ultrasound transmission member 16. The continuously decreasing tapering from the proximal to the distal direction shown in FIG. 3 allows for improved ultrasound energy propagation. The distal tip 36 can have a proximal section 46 which gradually increases in diameter until it reaches the proximal end of a distal section 48. The distal section 48 can have a bulbous configuration having a rounded or curved distal-most end that is adapted to contact the obstruction for ablation thereof. Thus, the distal tip 36 can have an enlarged size when compared to the rest of the ultrasound transmission member 16 so that the distal tip 36 can function as the distal head for the catheter 10.

In the embodiment shown in FIG. 2, the distal end 14 of the catheter body 11 has an opening 30, and the distal tip 36 of the ultrasound transmission member 16 is secured to the inner wall 62 of the main lumen 15 of the catheter body 11 adjacent the opening 30. The securement can be accomplished by an attachment mechanism 64 (which can be glue, welding or fusing) at the location of the proximal section 46 and the inner wall 62, so that part of the proximal section 46 is received inside the main lumen 15 and with the distal section 48 of the distal tip 36 extending outside the main lumen 15 of the catheter body 11. The opening 30 of the catheter body 11 is closed by the connection of the distal tip 36 to the catheter body 11. The construction shown in FIG. 2 directly attaches the ultrasound transmission member 16 to the catheter body 11 (via the attachment mechanism 64), which provides additional protection if the ultrasound transmission member 16 experiences breakage. In particular, if the ultrasound transmission member 16 fractures, breaks or splinters, the distal tip 36 will still remain secured to the catheter body 11 via the attachment device 64, and will not become dislodged from the catheter body 11. Thus, the embodiment of FIG. 2 does not employ a separate distal head for the catheter 10, but instead utilizes the distal tip 36 of the ultrasound transmission member 16 as a distal head which is secured directly to the distal end of the catheter body 11.

FIGS. 4-5 illustrate two different embodiments of a distal end of the catheter 10 which utilize the same principles and general construction as in FIG. 2, except that a distal cap is secured to the distal tip of the ultrasound transmission member. Therefore, the same numeral designations are used in FIGS. 2, 4 and 5 to designate the same or similar elements, except that an “a” and a “b” are added to the numeral designations in FIGS. 4 and 5, respectively. The differences between the embodiment of FIG. 2 and the embodiments in FIGS. 4 and 5 are described below.

The distal end 14 a in FIG. 4 differs from the distal end 14 in FIG. 2 in that a protective cap 66 a is secured to the distal section 48 a of the distal tip 36 a of the ultrasound transmission member 16 a. The cap 66 a can function as the tip of the catheter 10. The distal tip 36 a itself has a different configuration from the distal tip 36 in FIG. 2 in that the distal section 48 a is not bulbous or curved, but instead has a constant diameter that terminates distally at a flat distal end 68 a. The cap 66 a has a cylindrical configuration with an opened proximal end and a curved or bulbous distal end 70 a. The distal section 48 a of the distal tip 36 a is received into the hollow bore 72 a of the cap 66 a via the opened proximal end of the cap 66 a, and is secured to the cap 66 a inside the bore 72 a via an attachment device 74 a (which can be the same as the attachment device 64). The cap 66 a can be made of a radiopaque material to improve the visibility of the distal tip 36 a.

In addition, instead of the attachment mechanism 64, the embodiments of FIGS. 4-5 provide an intermediate member 64 a. The intermediate member 64 a can be a cylindrical component that is positioned around the ultrasound transmission member 16 a, and between the ultrasound transmission member 16 a and the inner wall 62 a of the catheter body 11 a. The intermediate member 64 a (as well as 64 and 64 b) is preferably made from a material that does not effectively transfer or conduct heat, and which is easy to attach to the ultrasound transmission member 16 a and the catheter body 11 a. Examples of the material can include certain epoxies, polymers, plastics and rubber. According to one embodiment, the intermediate member 64 a can be fused to the ultrasound transmission member 16 a and the inner wall 62 a. According to another embodiment, the intermediate member 64 a can be bonded to the ultrasound transmission member 16 a and the inner wall 62 a. According to yet another embodiment, the intermediate member 64 a can be fused to the ultrasound transmission member 16 a and bonded to the inner wall 62 a. The intermediate member 64 a serves as a safety feature to hold the ultrasound transmission member 64 a within the catheter body 11 in the event the ultrasound transmission member 16 a experiences breakage at a location proximal to the intermediate member 64 a. However, the intermediate member 64 a will not be able to hold the distal tip 36 a if the breakage occurs at the distal tip 36 a.

The distal end 14 b in FIG. 5 differs from the distal end 14 a in FIG. 4 in the following ways. First, the guidewire port 58 a, guidewire 25 a, and guidewire lumen 60 a have been omitted. Second, the distal tip 36 b itself has a different configuration from the distal tip 36 a in FIG. 4 in that a distal extension 76 b extends distally from the distal section 48 b. The distal extension 76 b has a smaller constant diameter than the diameter of the enlarged distal section 48 b, and the distal extension 76 b is received into the hollow bore 72 b of the cap 66 b via the opened proximal end of the cap 66 b, and is secured to the cap 66 b inside the bore 72 b via an attachment mechanism 74 b (which can be the same as the attachment mechanism 64). The cap 66 b can also be made of a radiopaque material to improve the visibility of the distal tip 36 b.

Third, the intermediate member 64 b in FIG. 5 has a different configuration as the intermediate member 64 a. The intermediate member 64 b has a generally conical configuration, having a wider diameter at its distal end 78 b (which resembles the base of the cone) and a narrower diameter or dimension at its proximal end 80 b (which resembles the narrowed tip of a cone). The hollow interior 82 b of the intermediate member 64 b has the greatest inner diameter adjacent its distal end 78 b and decreases to its smallest inner diameter adjacent the proximal end 80 b. This configuration for the intermediate member 64 b allows the ultrasound transmission member 16 b to be fitted and retained inside the hollow interior 82 b without the need to directly attach the ultrasound transmission member 16 b to the intermediate member 64 b. Specifically, the sections 46 b, 48 b can be retained inside the hollow interior 82 b, with the transition between the region 44 b and the distal tip 36 b (i.e., where the diameter of the ultrasound transmission member 16 b is the smallest) received in the narrow opening of the proximal end 80 b of the intermediate member 64 b. In other words, the proximal end 80 b overlaps a dimensional step (i.e., the transition between the region 44 b and the distal tip 36 b) on the ultrasound transmission member 16 b. The distal extension 76 b extends through another opening at the distal end 78 b of the intermediate member 64 b. To provide additional protection or safety, any or all of the sections 46 b, 48 b can also be bonded to the inner wall of the intermediate member 64 b. The outer surface 84 b of the intermediate member 64 b may be attached to the opened distal end of the catheter body 11 b by bonding, fusing or glue, and part of the intermediate member 64 b extends beyond the distal end of the catheter body 11 b.

Comparing the embodiments of FIGS. 4 and 5, the intermediate member 64 b has an “overlapped” configuration, which provides added protection because the intermediate member 64 b is seated on a dimensional step along the ultrasound transmission member 16 b, and will always hold the proximal portions of the ultrasound transmission member 16 b within the catheter body 11 b as long as the intermediate member 64 b is attached to the catheter body 11 b.

FIG. 6 illustrates a modification that can be made to the embodiment in FIG. 4. The embodiments in FIGS. 4 and 6 utilize the same principles and general construction, so the same numeral designations are used in FIGS. 4 and 6 to designate the same or similar elements, except that a “c” is added to the numeral designations in FIG. 6.

In FIG. 6, the catheter body 11 c, the guidewire port 58 c, the guidewire lumen 60 c, the guidewire 25 c, the ultrasound transmission member 16 c and the cap 66 c can be the same as the catheter body 11 a, the guidewire port 58 a, the guidewire lumen 60 a, the guidewire 25 a, the ultrasound transmission member 16 a and the cap 66 a in FIG. 4. The primary difference is that the intermediate member 64 a is now embodied in the form of an anchor wire 64 c, which can be either a polymer or a metal. One end 86 c of the wire 64 c can be attached (e.g., by glue, fusing, bonding) to the inner wall 62 c of the catheter body 11 c, and the other end 88 c of the wire 64 c can be attached (e.g., by glue, bonding or welding) to the distal tip 36 c and to the cap 66 c. If the ultrasound transmission member 16 c breaks at any location, then the ultrasound transmission member 16 c will be retained inside the catheter body 11 c.

FIG. 7 illustrates a modification that can be made to the embodiment in FIG. 6. Specifically, the embodiments in FIGS. 6 and 7 are the same except that the guidewire port 58 c, the guidewire lumen 60 c and the guidewire 25 c are omitted in FIG. 7, and the anchor wire 64 d is attached to the distal end of the ultrasound transmission member 16 d but not attached to the cap 66 d. Therefore, the same numeral designations are used in FIGS. 6 and 7 to designate the same elements, except that a “d” is added to the numeral designations in FIG. 7, and no further description of the elements in FIG. 7 is needed.

Attaching the anchor wire 64 c or 64 d to the cap 66 c or 66 d, or not attaching the anchor wire 64 c or 64 d to the cap 66 c or 66 d, provides different options. Attaching the anchor wire 64 c to the cap 66 c prevents dislodgement of the cap 66 c or the distal tip 36 c if the breakage occurs near or at the distal tip 36 c. However, breakage at such locations is rare, so the embodiment in FIG. 7 (where the anchor wire 64 d is not attached to the cap 66 d) can also be employed.

FIG. 8 illustrates another modification that can be made to the embodiment in FIG. 4. Specifically, the embodiments in FIGS. 4 and 8 are the same, except that the proximal portion of the cap 66 e has an annular edge 67 e that extends into the interior of the catheter body 11 e. Therefore, the same numeral designations are used in FIGS. 4 and 8 to designate the same elements, except that an “e” is added to the numeral designations in FIG. 8, and no further description of the elements in FIG. 8 is needed. The annular edge 67 e is not attached to the catheter body 11 e, and is maintained separate from the catheter body 11 e. One benefit which is provided by extending a portion of the cap 66 e into the catheter body 11 e is that this arrangement provides a smooth and friendly transition between the distal cap 66 e and the catheter body 11 e. This smooth transition facilitates navigation of the distal end 14 e through tortuous anatomy. Also, the non-affixed tip of the catheter body 11 e can result in the improved transmission of ultrasound energy from the transducer to the distal end 14 e.

FIG. 9 illustrates a modification that can be made to the embodiment in FIG. 5. Specifically, the embodiments in FIGS. 5 and 9 are the same except that the intermediate member 64 f is completely retained inside the catheter body 11 f, and the proximal portion of the cap 66 f has an annular edge 67 f that extends into the interior of the catheter body 11 f. Therefore, the same numeral designations are used in FIGS. 5 and 9 to designate the same elements, except that an “f” is added to the numeral designations in FIG. 9, and no further description of the elements in FIG. 9 is needed.

A guidewire has been included in the embodiments of FIGS. 2, 4, 6 and 8, while the guidewire has been omitted in the embodiments of FIGS. 5, 7 and 9. Embodiments showing the use or omission of a guidewire are shown for reference only. The principles of the present invention may be applied to catheters that include, or not include, a guidewire. The use or omission of a guidewire depends upon the choice of the clinician, and is often dictated by the access difficulty or specific clinical situations. For example, if the target lesion is located on a straight portion of the vessel, use of a non-guidewire embodiment will be feasible and relatively easy. On the other hand, if the target lesion is located in a tortuous location of the vessel, then use of a guidewire embodiment will help the clinician to navigate the distal tip 36 to the location of the lesion.

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 

1. An ultrasound catheter comprising: an elongate flexible catheter body having a proximal end, a distal end and a lumen extending longitudinally therethrough; and an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, with at least a portion of the distal end of the ultrasound transmission member extending outside the lumen of the catheter body and beyond the distal end of the catheter body, and with the ultrasound transmission member directly attached to the catheter body via an attachment device.
 2. The catheter of claim 1, wherein the attachment device is an adhesive.
 3. The catheter of claim 1, wherein the distal end of the ultrasound transmission member has a bulbous shape.
 4. The catheter of claim 1, wherein the distal end of the ultrasound transmission member has a dimensional step.
 5. The catheter of claim 1, wherein the attachment device is an intermediate member.
 6. The catheter of claim 5, wherein the intermediate member has a tubular configuration.
 7. The catheter of claim 1, wherein the attachment device is an anchor wire having one end that is attached to the catheter body and another end that is attached to the ultrasound transmission member.
 8. The catheter of claim 1, wherein the ultrasound transmission member is formed of a superelastic metal alloy.
 9. The catheter of claim 1, wherein the distal end of the ultrasound transmission member has a distal tip, with the attachment device attaching the distal tip to the catheter body.
 10. The catheter of claim 1, further including a cap positioned distal of the distal end of the catheter body and separate from the catheter body, with the cap secured to the distal end of the ultrasound transmission member.
 11. The catheter of claim 1, further including a guidewire lumen extending at least partially inside the lumen of the catheter body.
 12. The catheter of claim 11, wherein the guidewire lumen terminates at a guidewire port that positioned closer to the distal end of the catheter body than to the proximal end of the catheter body.
 13. The catheter of claim 12, wherein the guidewire port is positioned adjacent the distal end of the catheter body.
 14. The catheter of claim 9, wherein the distal tip of the ultrasound transmission member has a larger diameter than an intermediate region that is proximal of the distal tip.
 15. The catheter of claim 11, wherein the guidewire lumen extends concomitantly with the lumen.
 16. The catheter of claim 1, further including a fluid outlet port positioned at the distal end of the catheter body and communicating with the lumen.
 17. The catheter of claim 1, wherein the ultrasound transmission member is progressively tapered from its proximal end to its distal end.
 18. The catheter of claim 1, wherein the ultrasound transmission member also has a proximal region at its proximal end, and also has an intermediate region between the proximal and distal ends of the ultrasound transmission member, and wherein the distal end of the ultrasound transmission member has a larger diameter than the intermediate region.
 19. The catheter of claim 1, wherein the ultrasound transmission member irremovably attached to the catheter body via an attachment device.
 20. The catheter of claim 1, wherein the ultrasound transmission member movably attached to the catheter body via an attachment device.
 21. The catheter of claim 5, wherein the intermediate member is attached to the ultrasound transmission member and to the catheter body.
 22. The catheter of claim 5, wherein the intermediate member is attached to the ultrasound transmission member but is not attached to the catheter body.
 23. An ultrasound catheter comprising: an elongate flexible catheter body having a proximal end, a distal end and a lumen extending longitudinally therethrough; an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, and with the ultrasound transmission member directly attached to the catheter body via an attachment device; and a cap positioned distal of the distal end of the catheter body and separate from the catheter body, with the cap secured to the distal end of the ultrasound transmission member.
 24. The catheter of claim 23, wherein the cap has a larger outer diameter than the catheter body.
 25. The catheter of claim 23, wherein the cap is partially positioned inside the catheter body.
 26. An ultrasound catheter comprising: an elongate flexible catheter body having a proximal end, a distal end and a lumen extending longitudinally therethrough; an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, with at least a portion of the distal end of the ultrasound transmission member extending outside the lumen of the catheter body and beyond the distal end of the catheter body; a cap attached to the distal end of the ultrasound transmission member; and an attachment device that attaches the cap to the catheter body.
 27. The catheter of claim 26, wherein the attachment device is an anchor wire having one end that is attached to the catheter body and another end that is attached to the cap.
 28. A method of ablating tissue in a vessel, comprising: a. providing an ultrasound catheter comprising: an elongate flexible catheter body having a proximal end, a distal end and a lumen extending longitudinally therethrough; and an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, with at least a portion of the distal end of the ultrasound transmission member extending outside the lumen of the catheter body and beyond the distal end of the catheter body, and with the ultrasound transmission member directly and irremovably attached to the catheter body; and b. causing the distal end of the ultrasound transmission member to directly contact the tissue.
 29. The method of claim 28, further including: providing an intermediate member that attaches the ultrasound transmission member to the catheter body.
 30. A method of ablating tissue in a vessel, comprising: a. providing an ultrasound catheter comprising: an elongate flexible catheter body having a proximal end, a distal end and a lumen extending longitudinally therethrough; and an ultrasound transmission member extending longitudinally through the lumen of the catheter body, the ultrasound transmission member having a proximal end that is coupled to a separate ultrasound generating device, and a distal end that terminates at the distal end of the catheter body, with at least a portion of the distal end of the ultrasound transmission member extending outside the lumen of the catheter body and beyond the distal end of the catheter body, and with the ultrasound transmission member directly attached to the catheter body; a cap positioned distal of the distal end of the catheter body and separate from the catheter body, with the cap secured to the distal end of the ultrasound transmission member; and b. causing the cap to directly contact the tissue.
 31. The method of claim 30, further including: providing an intermediate member that attaches the ultrasound transmission member to the catheter body. 